8. HOW DO ORGANISMS REPRODUCE .
Questions:
1. The correct order of binary fission in Leishmania is
(a) II, III, IV, I (b) I, III, IV, II (c) IV, I, III, II (d) III, I, II, IV
Ans: (b) I, Ill, IV, II
2. What is DNA?
Ans: DNA is the carrier of hereditary information from parents to the next generation. Hereditary material is present in all living cells.
3. What is vegetative propagation?
Ans: It is a type of propagation in which new plants are obtained from the parts of old plants like stems, roots and leaves, without the help of any reproductive organ.
4. Name the method by which Hydra reproduces. Is this method sexual or asexual?
Ans: Hydra reproduces by Budding. It is an asexual reproduction.
5. “Cell division is a type of reproduction in unicellular organism”. Justify.
Ans: During cell division in unicellular organisms, the nucleus of the parent cell divides only once to form two daughter nuclei along with the cytoplasm that undergoes cleavage. In this way, two daughter cells are formed from one single parent.
6. List four advantages of vegetative propagation.
Ans: (i) Only one parent is required for reproduction, this eliminates the need of special mechanisms.
(ii) Many plants are able to tide over unfavourable conditions. (iii) Plants that can not produce seeds are propagated by this method.
(iv) The trait of the parent plant is preserved.
7. How is the process of binary fission different in Amoeba and Leishmania?
Ans: Amoeba reproduces through simple binary fission. Leishmania reproduces asexually through binary fission that occurs along a definite orientation related to the whip like structure at one end of the cell.
8. “Tissue culture helps to improve the nations’ economy”. Justify.
Ans: (i) Tissue culture is extensively used for large scale propagation of medicinal and ornamental plants. V
(ii) It is also used for propagation crop and forest plants.
(iii) It is also used for developing disease - free plants.
(iv) Cell culture is particularly used for extracting ion of many useful metabolites.
9. The picture given below depicts the process of asexual reproduction in Plasmodium.
(i) Name the process depicted above and define it.
(ii) What is meant by asexual reproduction?
Ans: (i) Multiple Fission. It is a division of single-celled organisms into many daughter cells simultaneously. (ii) Creation of a new generation from a single individual or a single parent is involved.
10. Write one main difference between asexual and sexual mode of reproduction. Which species is likely to have comparatively better chances of survival-the one reproducing asexually or the one reproducing sexually 7 Justify your answer.
Ans: Asexual reproduction does not involve genetic fusion while sexual reproduction involves fusion of male and female gametes to form a zygote. (i) Species reproducing sexually have better chances of survival. 1 (ii) Reason-Sexual reproduction gives rise to more variations which are essential for evolution as well as survival of species under unfavourable conditions.
11. What is the effect of DNA copying, which is not perfectly accurate, on the reproduction process? How does the amount of DNA remain constant though each new generation is a combination of DNA copies of two individuals?
Ans: Reproduction results in the production of offspring similar to parents in body design and form. The exact blue prints of body design is inherited in the offspring due to DNA replication/DNA copying. The imperfect DNA copying results in genetic variations that can be both useful or harmful for the offspring. The useful variations gets selected in nature and helps organism to survive in the changing environment while harmful variation gets eliminated.
If each new generation is to be the combination of the DNA copies from two pre-existing individuals, then each new generation will end up having twice the amount of DNA that the previous generation had. In sexual reproduction, the gametes usually contain half number of chromosomes and same numbers present in the body cells. These haploid gametes when fuse produce a new cell with double number of chromosomes than the gametes and same as the body cells. In this way organisms restrict doubling of DNA and maintain the chromosome number.
12. List three distinguishing features between sexual and asexual type of reproduction, in tabular form.
Ans: Differences between Sexual and Asexual reproduction:
13. (i) Identify the process depicted in the diagram given below.
(ii) The part labelled as spores has a covering of thick walls around it. What is its advantage?
(iii) What are hyphae?
Ans: (i) Spore formation in Rhizo pus.
(ii) The thick walls protect the spores until they come in contact with soil.
(iii) The thread like projections are called hyphae.
14. What is vegetative propagation? List with brief explanation two advantages of practising this process for growing same types of plants. Select two plants from the following which are grown by this process: Banana, Wheat, Mustard, Jasmine, Gram.
Ans: (a) Vegetative propagation is the development of a new plant from the vegetative parts / roots, stem and leaves of a plant.
(b) Advantages: (i) Such plants can bear flowers and fruits earlier than those produced from seeds
(ii) Allows propagation of plants (banana, orange etc) that have lost capacity to produce seeds.
(iii) Jasmine, banana.
15. Differentiate between the following:
(i) Pollen tube and style. (ii) Fission in Amoeba and Plasmodium Pollen Tube Style
16. What is the function of pollen grains in flowers?
Ans: Pollen grains fertilise the egg cell present in the embryo sac.
17. What is the function of petals in a flower?
Ans: The functions of petals is to attract insects for pollination and to protect the reproductive organs, which are at the centre of the flower.
18. Why is fertilization not possible without pollination?
Ans: Pollination allows pollen grains that produce male germ cell to reach the carpel which contain the female germ cell, egg. Thus fertilization which involves fusion of male and female germ cells can only occur after pollination.
19. Explain giving one example of each, the unisexual and bisexual flowers.
Ans: Unisexual is the plant whose flowers contain either stamens or carpels but not both Example: Papaya, watermelon, Bisexual is the plant whose flowers contain both stamens and carpels. Example: Hibiscus, Mustard.
20. How is the process of pollination different from fertilization?
Ans: Pollination is the transfer of pollen grains from anther to the stigma of a flower Fertilization is the fusion of male and female gametes.
21. Draw a labelled longitudinal structure of a flower showing its parts.
Ans:
22. Name the parts A, B and C shown in the diagram and write their functions. [SSLC July 2018-19]
Ans: Part A is Stigma. Function: It is the terminal part of carpel, which may be sticky and helps in receiving the pollen grains from the anther of stamen during pollination. Part B is
Pollen tube.
Function: The pollen tube grows out of the pollen grain through the style to reach the ovary. Part C is Female Germ Cell.
Function: It is a female gamete which fuses with male gamete to form a diploid cell known as zygote.
23. What is a seed? How does it help in reproduction in plants? Seed
Ans: A seed is the reproductive unit of a plant which can be used to grow into a new plant. It contains body plant or embryo and food for the baby plant. The baby plant present in a seed is in the dormant or inactive state. When the seeds get suitable conditions of water, warmth, air and light, then new plants grow out of these seeds. In this way, the parent plant reproduces more plants like itself by forming seeds through flowers.
24. (i) Draw a neat labelled diagram of a germinated seed and label radicle, plumule and cotyledon. (ii) Mention function of each of these parts.
Ans: (i)
(ii) (a) Radicle Future root, (b) Plumule : Future stem, (c) Cotyledon (food store).
25. (i) Define the terms pollination and fertilisation.
(ii) Distinguish between self pollination and cross pollination.
Ans: (i) Pollination: It is the transfer of pollen grains from the anther of a stamen to the stigma of a carpel. Fertilisation: It is defined as the fusion of a male gamete with a female gamete to form a zygote during sexual reproduction.
(ii) Difference between self pollination and cross pollination
26. Draw a longitudinal section of a flower and label the following parts:
(i) Part that develops into a fruit
(ii) Part that produces pollen grain
(iii) Part that transfers male gametes (iv) Part that is sticky to trap
Ans: A
27. No two individuals are absolutely alike in a population. Why?
Ans: Because hundreds of biochemical reactions occur during preparation of DNA copies. Few of them are liable to run and form a different product and hence they are not identical to the original. Thus, this gives rise to variations.
28. What is placenta? Write any two major functions of placenta. [SSLC July, 2018-19]
Ans: A disc shaped organ or special tissue in the uterus of pregnant mammal, nourishing and maintaining the foetus through the umbilical cord. Functions of Placenta: (i) Helps in the transportation of glucose and oxygen from the mother to the embryo. (ii) Helps in removal of waste generated by the embryo
29. (a) Draw a sectional view of human female reproductive system and label the part where (i) Eggs develop (ii) Fertilization take place
(iii) Fertilized egg gets implanted. (b) Describe, in brief, the changes the uterus undergoes (i) To receive the zygote.
(ii) If zygote is not formed.
Ans: (a) The human female reproductive system consists of a pair of ovaries, a pair of oviducts, the uterus and the vagina.
(i) The development of egg occurs in the ovary.
(ii) Fertilisation takes place in the fallopian tubes.
(iii) The fertilised egg gets implanted in the uterus.
(b) (i) The uterus prepares itself every month to receive a fertilized egg/zygote. The inner uterus lining (endometrium) becomes thick and is supplied with blood to nourish the embryo.
(ii) If the egg is not fertilised, then the uterus lining is not required. Hence, it breaks down and gets released in the form of blood and mucous through the vagina. This process lasts for 2—8 days. This cycle occurs every month and is known as menstruation.
30. Why is variation beneficial to the species but not necessarily for the individual?
Ans: Variations are beneficial to the species than individual because sometime for a species, the environmental conditions change so drastically that their survival becomes difficult. During that period, only few variants that are resistant would be able to survive. Thus, variants help in survival of the species. However, all variations are not necessarily beneficial for the individual organisms.
Textbook Exercises
1. Asexual reproduction takes place through budding in
(a) Amoeba (b)Yeast (c) Plasmodium (d) Leishmania
Ans: (b) Yeast
2. Which of the following is not a part of the female reproductive system in human beings?
(a) Ovary (b) Uterus (c) Vas deferens (d) Fallopian tubes
Ans: (c) Vas deferens
3. The anther contains
(a) Sepals (b) Ovules (c) Pistil (d) Pollen grains
Ans: (d) Pollen grains
4. What are the advantages of sexual reproduction over asexual reproduction?
Ans: (i) The offspring exhibit diversity of characters as the fusing gametes come from two different and sexually distinct individuals.
(ii) Meiosis during gametogenesis provides opportunities for new combination of genes.
5. What are the functions performed by testis in human beings?
Ans: The testis produce sperm and also male sex hormone testosterone.
6. Why does mensuration occur?
Ans: When the egg is not fertilised, menstruation occurs in human females.
7. Draw a labelled diagram of longitudinal section of a flower?
8. What are the different methods of contraception?
Ans: (i) Barrier method or mechanical method! Condom/Diaphragm, to prevent the meeting of sperms and ova.
(ii) Chemical method/ Oral pills— Changes the hormonal balance of the female partner so that the eggs are not released.
(iii) Surgical method - to block the vas deferens in males/vasectomy or the fallopian tube (oviduct) in females/ tubectomy, to prevent the transfer of sperms or egg and hence no fertilization takes place.
(iv) IUCDs/ Loop or the copper-T placed in the uterus, to prevent pregnancy.
9. How are the modes of reproduction different in unicellular and multicellular organisms?
Ans: Unicellular organisms reproduce asexually whereas multicellular organisms reproduce sexually.
10. How does reproduction help in providing stability to population of species?
Ans: Living organisms reproduce for the continuation of a particular species. It helps in providing stability to the population of species by producing new individual that resembles the parents.
11. What could be the reasons for adopting contraceptive methods?
Ans: Frequent and unwanted pregnancies can be avoided by adopting contraceptive methods. Also, these methods check population growth by controlling childbirth rate.
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